Phosphorus intake by a person originates from dietary sources, such as meat, dairy products and soft drinks. Protein sources account for a significant portion of phosphorus intake. See R. A. Sherman, and O. Mehta, Dietary Phosphorus Restriction in Dialysis Patients: Potential Impact of Processed Meat, Poultry, and Fish Products as Protein Sources, American Journal of Kidney Diseases, Vol. 54, No 1 pp. 18-23 (2009). Phosphorus (P) accumulates in patients with renal insufficiency due to lack of excretion of phosphorus by the kidney. Patients who have chronic kidney disease (CKD) stages 1-4 have some native kidney function that decreases as the disease progresses. Stage 5 is considered kidney failure, at which point some renal replacement therapy such as, for example, hemodialysis is needed. During the initial stages of CKD, patients may be able to maintain serum phosphorus concentrations within acceptable levels; however, as CKD progresses this may become more difficult, requiring the use of phosphate binder therapy. The patient is then prescribed an intake of phosphate (PO4) binders, such as calcium acetate (e.g., PhosLo®) or calcium carbonate, that is intended to maintain the phosphorus concentration in the patient's blood to a normal or near normal level, typically between about 3.5 and about 5.5 mg/dL, preferably about 4.5 mg/dL. The phosphate binder converts the phosphorus ingested by the patient into a bound (phosphate) form that cannot be absorbed and is therefore eliminated from the patient's body. Additionally, patients who have started hemodialysis treatment may still have some residual native kidney function. This residual renal function will be an additional means of phosphorus removal for such patients. In order to estimate the magnitude of this removal, the amount of phosphorus contained in urine for patients with a range of residual renal function needs to be measured.
For patients with end stage renal disease (ESRD), the excess phosphorus is often not sufficiently eliminated by dialysis treatments. Consequently, nearly all ESRD patients develop hyperphosphatemia. See J. T. Daugirdas, P. G. Blake, and T. S. Ing, Handbook of Dialysis, (2007). Increased phosphorus levels have a significant role in the high mortality rate observed in the population of patients on long-term dialysis therapy. B. Kestenbaum, Phosphate metabolism in the setting of chronic kidney disease: Significance and recommendations for treatment, Semin. Dial. Vol. 20, pp. 286-294 (2007).
An ongoing challenge for patients with renal insufficiency is the daily pill burden and its relation to health-related quality of life. One study found that about half of the daily pill burden in maintenance dialysis patients is due to prescribed phosphate binders, and only 38% of the patients were adherent to the prescribed phosphate binder therapy, with a higher pill burden from phosphate binders being associated with lower adherence. Y. W. Chiu, I. Teitelbaum, M. Misra, E. M. de Leon, T. Adzize, and R. Mehrotra, Pill burden, adherence, hyperphosphatemia, and quality of life in maintenance dialysis patients, Clin. J. Am. Soc. Nephrol., Vol. 4, pp. 1089-1096 (2009).
Therefore, a method is needed to identify the patients that are non-compliant with a prescribed diet and/or a phosphate binder regimen, in order to aid the physician in making clinical decisions.